There are a few components of the current signal that may lead to inaccurate current measurement in power systems, and therefore, may cause malfunction on numerical protective relays and control devices. Some of these components include harmonics, the decaying DC offset, and noises. In this study, a phasor estimation method based on artificial neural networks is proposed, which will provide fast response time and accuracy. The method uses the multilayer perceptron structure to precisely estimate the amplitude and phase angle of the current waveform by determining its input weights during an online training process. The proposed algorithm is tested and compared with other reliable and well-known methods for a performance evaluation.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-smt.2014.0312

Phasor estimation in power systems using a neural network with online training for numerical relays purposes

Orthogonal frequency division multiplexing (OFDM) techniques are attractive for underwater acoustic (UWA) communications due to their robustness against large multipath spread. However, OFDM systems in UWA channels suffer from intercarrier interference (ICI) caused by the Doppler effect. In this paper, we propose an effective mirror-mapping-based ICI self-cancellation method in OFDM UWA communications. Theoretical analyses and numerical results show that the proposed mirror-mapping-based ICI self-cancellation schemes can effectively reduce the carrier-to-interference power ratio (CIR) in comparison with the plain OFDM scheme in the additive white Gaussian noise (AWGN) channel with carrier frequency offset (CFO). To demonstrate their benefits for OFDM UWA communications, the mirror-mapping-based ICI self-cancellation schemes were tested in a recent sea experiment, conducted in Taiwan in May 2013. The decoding results show that the mirror-mapping-based ICI self-cancellation schemes improve the BER performance of the OFDM system considerably in UWA channels.

Effective self-cancellation of intercarrier interference for OFDM underwater acoustic communications

Fast time-varying, phase variation, and Doppler shift constitute the features of the underwater acoustic (UWA) communication channel. As a consequence, the effect of intercarrier interference (ICI) becomes significantly critical for orthogonal frequency division multiplexing (OFDM) based UWA communication systems. In this paper, an ICI countermeasure, termed two-path transmission, is proposed. The key idea is to employ data repetition within two concatenated OFDM blocks according to subcarrier mirror mapping criterion. Through theoretical analysis and numerical results, it is shown that the proposed two-path transmission schemes can effectively improve the carrier-to-interference power ratio (CIR) in the presence of carrier frequency offset (CFO) and additive white Gaussian noise (AWGN). Furthermore, a recent sea experiment conducted in Taiwan in May 2013 verifies the ICI suppression capability of the proposed schemes in UWA channels.

Effective intercarrier interference reduction techniques for OFDM underwater acoustic communications

Synchronized Phasor measurement units (PMUs) are of prime necessity in the Smart Electric Grid Architecture. Knowledge on voltage and current Phasor helps in power system state estimation, monitoring and control. This paper deals with the development of a laboratory prototype of PMU. Synchrophasor estimation algorithms are modelled using LabVIEW. The model is burned into FPGA based controller to achieve an online Phasor measurement system. The developed prototype is used against a dynamic transmission system model consisting of single phase voltage source connected to a load by a transmission line. The paper also studies the effect of the line impedance on the Phasor estimates. Finally, the accuracy of the Phasor estimate from the developed model is verified.

Laboratory prototype of a phasor measurement unit using FPGA based controller

Underwater acoustic (UWA) communication channel features relatively fast time variation. Spatial modulation (SM) combined with orthogonal frequency division multiplexing (OFDM) transmission can be applied to UWA communications. Channel estimation may induce a performance penalty for SM since only one transmit antenna is activated to carry pilots. Recently, a differential solution has been proposed for SM, which dispenses with channel estimation and restricts the signal-to-noise (SNR) loss to a relatively low level under quasi-static channel conditions. Hence, the application of differential SM (DSM) to OFDM UWA communications is of particular interest. Simulation results show that when applied to UWA communications, DSM has an obvious performance enhancement in bit error rate (BER) over SM.

Differential spatial modulated OFDM in underwater acoustic communications

Frequency and phasor are two important parameters for power system monitoring and operation. While most frequency and phasor estimation algorithms are developed separately and only work for complex-valued signals, we propose an iterative joint frequency and phasor estimation method for real-valued signals in power systems. Our proposed method is tested alongside existing algorithms using both numerically by simulations and the experimentally by OpenPMU system, an open source platform for synchronized PMU and smart grid research. The comparisons show that our proposed method not only beats existing single-task algorithms for steady-state signals but also tracks the transient signals with time-varying frequency very well.

A Joint Frequency and Phasor Estimation Algorithm Using DFT Samples for Power Systems

For underwater acoustic communications (UAC), the bandwidth is wide compared with the carrier frequency. Because of this fact, the advantages of using multiband OFDM (MB-OFDM) for ultra-wideband communications in terrestrial environments may also apply to UAC scenarios. In this paper, a comparison is made between the use of single-band OFDM and MB-OFDM for UAC. The complexity of each method is shown and experimental results from the WHOI09 undersea trial are presented for both single-band and multiband schemes. From the analysis and experimental results, the validity of treating UAC as ultra-wideband can be determined and the comparative advantages and disadvantages of MB-OFDM versus single-band OFDM for UAC discovered.

Robert Griffin

Papers

A Joint Frequency and Phasor Estimation Algorithm Using DFT Samples for Power Systems

Multi-band OFDM for underwater acoustic communications